Dibasic acid esters of glycols



United States Patent ,DIBASIC ACID ESTERS 0F GLYCIOLS Paul 'V. Smith, Jr., Sunningdale, England, assigns: to

E'sso Research and Engineering Company, a corporation of Delaware No Drawing. Original No. 2,703,811, dated March 8, 1955, Serial No. 52,429, October 1, 1948. Application for reissue November 19, 1956, Serial No. 623,269

8 Claims. (Cl. 260-485) Matter enclosed in heavy brackets appears in the original patent but. forms no part of this reissue specification; matter printed in italics indicates the additions madenby reissue.

This invention relates to a new class of compounds which have beentfoundato be particularly suitable for use as synthetic lubricants because of their low pour points and high viscosity indices.

Inthe lubricant art, considerable progresszhas been realized in recent years in the production of lubricants characterized by one or more specific properties and adapted for particular uses. In the main, this-progress can. be attributed ;to two developments: the first, new :re fining, procedures, and the second, addition agents ca-' pable; of imparting; particular properties to available lubricants. Thus, viscosity index improvers and pour depressants are added to automotivelubricants to .render thelubricants. more adaptable to wide changes in' temperature. conditions, while other agents areadded toiimprove the load-carrying properties-of a lubricant which is-z to be employed, for example, under extreme pressure conditions.

Recently, in an efiort to obtain superior lubricants endowed withspecific and superior characteristics, anew field has-been exploded, namely the synthesis of lubricants from-various materials. Esters representoneclass of materials which have attracted unusual interestas synthetic. lubricants. In general, they are characterized by higher viscosity indices and lower pour points-than mineral oils of. corresponding viscosity. The esterjs'described in the'present specification have beenfound to exhibitvery low pour points and high viscosity indices. Lubricants possessing such properties are of special value in the lubrication of engines which are subjectedto high temperatures, such as combustion turbine engines, particularly thoseof the prop-jet type.- Mineral'oil-lubrh cants. containing added viscosity index improvers, thickeners or other highly non-volatileadditives are .undesirable for use in such engines because of the tendency to .leave a residue which accumulates and'interferes with the operation of the engine. A synthetic lubricant of the type described in the present specificationis especially adapted to use under such conditions, .sincethelubricant contains no additives and thus: tends to leave .no. residue upon volatilization.

Re. 24,287 Reissued Mar. 12, 1957 The new compounds of the present invention which have been found to be particularly suitable for use as lubricating oils are complex esters prepared by reacting one mol of a monohydric alcohol with one mol of a dibasic acid, thereby forming the half-'ester'of the dibasic acid, after which two mols of such half-ester are reacted with one mol of a glycol. The new class of compounds may be broadly defined by the following general formula:

/CO0R: R1

coo

wherein R1 and R1" are aliphatic hydrocarbon radicals, straight'cliain or branched, saturated or unsaturated,- each containing 0 to 30 carbon atoms, or they may be organic radicals" consisting of a series of saturated aliphatic hydrocarbon radicals interlinked by atoms of oxygen or sulfur, or both oxygen and sulfur, provided there are at least 2 carbon atoms between eachpair of oxygen or sulfur atoms, and not more than 2 atoms of sulfur in each chain, and provided further that the total number of carbon, oxygen, and sulfur atoms in each radical is from 3 to 40. R2 and R2 of the formula represent monohydric alcohol residues which may each be (1,) a saturated straight chain aliphatic hydrocarbon radical containing not more than" 5 carbon atoms, (2) a saturated branched chain hydrocarbon radical containing 3 to 20 carbon atoms, or (3) a series of saturated aliphatic hydrocarbon radicals, straight chain or branched, interlinked by oxygen or sulfur atoms, or both oxygen and sulfur atoms, the total numberof carbon, oxygen, and sulfur atoms being from 4 to 20, and the number of oxygen of sulfur atoms or both'in the radical being not more than 5. There should also be a chain of at least 2 carbon atoms between'the acid radical and the first oxygen of sulfur atom and a similar chain of at least 2 carbon atoms between each pair of oxygen or'sulfur atoms in the radical. R3 of the formula represents a glycol radical, and it may consist of a saturated aliphatic hydrocarbon group, straight chain or branched, containing 2 to 20 carbon atoms, or it may be a series of saturated alip'hatichydrocarbon radicals interlinked by oxygen or sulfur atoms, or by both oxygen and sulfur'atoms, provided there are at least 2 carbon atoms between each carboxyl group and the nearest oxygen-or sulfur atom and at least 2 carbon atoms between ea'ch pair of oxygen or sulfur atoms in the chain. The total number of carbon, oxygen, and sulfur atoms in the entire R3 radical is from 5 to and the number of sulfur atoms is not greater than 2. 'Do provide a producthaving sufiicient viscosity for lubricating purposes the" molecular weight 'of the entire'este'r should be; atleast 300, and to provide a product having-a pour point sufiiciently low, i. e., an A. S. T. M. pour point not higher than B, it is generally necessary that the molecule contain at least 2 atoms of oxygen or sulfur, or both oxygen and sulfur, in ether or thioether linkages.

Among the various components of the complex esters of the present invention certain preferences may be pointed out as giving the optimum of desired properties from the standpoint of service as a lubricant. The preferred dibasic acids are the straight chain dibasic acids of the parafiinic group having from 6 to 10 carbon atoms per molecule. The preferred glycols are the polyethylene glycols of the formula HO (CHzCHzO 11CHzCH2OI-I where n is 1 to 26.

Illustrative examples of the dibasic acids which may be employed in the synthesis of the complex esters of the present invention are the following:

The C4-C24 alkenyl succinic acids listed above are prepared by condensing olefins or mixtures of olefins with maleic anhydride.

The monohydric alcohols employed are typified by the following:

Methyl alcohol Ethyl alcohol n-Butyl alcohol Z-ethylhexyl alcohol Ethylene glycol mono-n-butyl ether Ethylene glycol mono-Z-ethylbutyl ether Ethylene glycol mono-Z-ethylhexyl ether Ethylene glycol mono-tert.-octyl ether fl-n-Butylmercaptoethanol )8-Tert.-octylmercaptoethanol fi-n-Dodecylmercaptoethanol Diethylene glycol mono-n-butyl ether =Diethylene glycol mono-2-ethylbutyl ether Diethylene glycol mono-Z-ethylhexyl ether Propylene glycol mono-butyl thioether Propylene glycol mono-tert.-octyl thioether Propylene glycol mono-n-dodecyl thioether n-Butylmercaptoethoxyethanol Tert.-octylmercaptoethoxyethanol n-Dodecylmercaptoethoxyethanol n-Butylmercaptopropoxypropanol Tert-octylmercaptopropoxypropanol n-Dodecylmercaptopropoxypropanol Propylene glycol mono-n-butyl ether Dipropylene glycol monomethyl ether Dipropylene glycol monoethyl ether Dipropylene glycol mono-n-butyl ether Tripropylenc glycol monomethyl ether Tripropylene glycol monoethyl ether Tripropylene glycol mono-n-butyl ether Propylene glycol monoisopropyl ether Dipropylene glycol monoisopropyl ether Tripropylene glycol monoisopropyl ether Many of the above listed ether alcohols, formed by the reaction of ethylene oxide or propylene oxide with aliphatic alcohols, are known in the industry as Dowanols, "Carbitols, or Cellosolves.

A group of alcohols especially adapted for use in the present invention are the so-called 0x0 alcohols, prepared by the reaction of carbon monoxide and hydrogen upon the olefins obtainable from petroleum products. Materials such as diisobutylene and C1 olefins are suitable for this purpose, also higher weight olefinic materials are sometimes employed. The alcohols obtained in this manner normally have a branched chain structure. The Oxo process for the preparation of alcohols was developed in Germany and first described in this country in Roelen U. S. Patent No. 2,327,066, granted August 17, 1943.

The glycols employed in preparing the esters of the present invention include ethylene glycol and any of the paraffinic homologues of the same containing up to 20 carbon atoms. These homologues may include, for example, propylene glycol, butylene glycols, pinacone, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, and the like. Since the glycols may also contain oxygen or sulfur atoms, compounds such as diethylene glycol, triethylene glycol, the polyethylene glycols of the formula H0 (CHzCHzO) nCHZCHZOH where n is 1 to 26, and the polypropylene glycols of the general formula where R or R is a methyl group and the other is hydrogen and where n is 1 to 20, may likewise be employed. Glycols containing sulfur atoms in thioether linkages may also be employed, and these include such compounds as thiodiglycol and 1,2 bis(2 hydroxyethylmercapto)ethane. There also may be used glycols containing both oxygen and sulfur in similar linkages; such as a compound is bis- 2- (Z-hydroxyethoxy) ethyl] sulfide.

It will be understood that when glycols are employed which contain no oxygen or sulfur in the chain, at least two such non-carbon atoms should be introduced into the molecule by means of the acid or monohydric alcohol employed in the esterification, since these non-carbon atoms are required for producing products of sufiiciently 10w pour point, as stated above.

If desired, various addition agents may be incorporated in the esters of the present invention for the purpose of improving their properties with respect to their usefulness as lubricants. For example, antioxidants, viscosity index improvers, thickeners, pour depressants, dyes, etc., may be added.

Data will be given below showing the properties of several examples of complex esters within the scope of the present invention, indicating the adaptability of these esters to lubricating service. All of these esters were prepared by a general esterification method which may be described in detail as follows: In a 1-liter round bottom reaction flask, fitted with a reflux condenser and water trap, were placed 0.5 mol of dibasic acid, 0.5 mol of monohydric alcohol, 1.5 grams of p-toluene-sulfonic acid monohydrate (catalyst), and ml. toluene. The mixture was refluxed until no more water collected in the water trap. After cooling, 0.25 mol of a glycol was added and the refluxing process resumed until again no more water collected in the trap. The mixture was washed with three l00-ml. portions of saturated aqueous sodium car bonate solution and one IOO-ml. portion of water. After drying with Drierite (anhydrous calcium sulfate) the material was filtered and stripped at a pressure of about 12 mm. to a bath temperature of about 225 C.

The results of tests of various properties of esters prepared by the above general method are shown in the table of data which follows.

Flash eosity Components of Ester Kinematic Vis- ASTM Slope Viscoslty Index Adiplc acid n-Butyl alcohoL Trimethylene glycol Adiplc acid n-Butyl alcohol 'Irlethyleue Adlpic acid Os x0" alcohol.

| MMWMMWWWMW Tetraethylene glyool Adlplc acid Ethylene glycol monoethyl ethen. 385 25.010

hlodlglycol Adiplo acid---" Dipropileue glycol monolsopropyl ethe 'Ietraet ylene glycol Adipic acid CI 020" 455 48. S00

Triethylene glycol- 14-01: alkel l yl succinic acid".

alco

Tetraethylene glyc Thiodipropionic aeid n-Butyl alcohol Trlmethylene glycol Prepared by condensing a 011-018 olefin mixture with maleie anhydridc.

wherein R1 and R1 are straight chain aliphatic hydrocarbon groups each containing from 0 to 8 carbon atoms, wherein R2 and R2 are branched chain aliphatic hydrocarbon groups containing from 4 to 20 carbon atoms each, :at least one of said groups containing at least one atom of the group of oxygen and sulfur in ether linlcage, and wherein R3 is a radical of the formula (CHaCH20)nCHzCHzwherein n is a number of from 1 to 26, the components of the composition being so chosen that the molecular weight thereof is at least 300.

2. A composition according to claim 1 wherein R1 and R1 contain from 7 to 8 carbon atoms and wherein n is from 3 to 8.

[3. A composition according to claim 1 wherein R2 and R2 are derived from ethylene glycol monoethyl other] 4. A composition according to claim 1 wherein R2 and R2 are derived from dipropylene glycol monoisopropyl ether.

5. As a new composition of matter, a compound of the formula RzOOC (CH2) xCOO (CHaCHzO )nOC(CH2)xCOOR2 wherein R2 is a branched chain aliphatic hydrocarbon radical of from 4 to 13 carbon atoms, wherein x is a number of from 7 to 8, and wherein n is a number of from 3 to 8.

6. A compound according to claim 5 wherein R2 contains about 8 carbon atoms.

7. A compound according to claim 5 wherein x is about 8.

8. A compound according to claim 5 wherein n is about 4.

9. As a new composition of matter, a compound of the formula CaH17OOC(CH2)aCOO(CH2CH20)4OC (CH2) sCOOHnCa References Cited in the file of this patent or the original patent UNITED STATES PATENTS 2,023,485 Malm Dec. 10, 1935 2,075,107 Frazier Mar. 30, 1937 2,295,165 De Groote Sept. 8, 1942 2,363,045 De Groote Nov. 21, 1944 2,375,529 De Groote May 8, 1945 2,379,251 Muskat June 26, 1945 2,392,621 Strain Ian. 8, 1946 2,415,366 Muskat Feb. 4, 1947 2,628,974 Sanderson Feb. 17, 1953 2,668,848 Neuworth Feb. 9, 1954 

